All reported sexually transmitted infections have been from men to women.

After 3 reported cases of possible sexual transmission of Zika virus, the Centers for Disease Control and Prevention (CDC) has released interim guidelines to prevent sexual transmission. The guidelines are aimed at men who have traveled to or reside in areas of ongoing transmission and their sex partners.

There is currently no report of the virus spreading from infected women to their sex partners. However, pregnant women who have male partners that traveled to or reside in areas of transmission are advised to discuss their partner's potential exposure to mosquitoes, and history of Zika-like illnesses with their healthcare provider.

Precautionary measures, such as abstaining from sexual activity or using condoms consistently and correctly during sex are advised for men who reside in or have traveled to an area of active Zika virus transmission and have partners who are pregnant or non-pregnant. These are particularly important in the case of Zika virus as infection is mostly asymptomatic, and when illness does occur, it is usually mild and lasts for only a few days. The risk of sexual transmission is increased as the virus may persist in semen when it is no longer detectable in blood.

Of the possible sexually transmitted cases known, the first was transmitted from a man to a woman, in which sexual contact occurred a few days before the man's symptom onset. The second is a case of sexual transmission in Texas, currently under investigation, and the third is a single report of replication-competent Zika virus isolated from semen from 2 weeks to possibly 10 weeks after illness onset.

In the third case, where the virus was isolated in semen, blood tests collected at the same time did not detect the virus. No further testing has been conducted and so the duration of Zika virus in semen remains unknown. It is also unknown whether asymptomatic men can transmit Zika virus to their partners. Currently, testing of men to assess risk for sexual transmission is not recommended. Recommendations to prevent sexual transmission of Zika virus will continue to be updated as more information on the incidence and duration of seminal shedding from infected men become available.